1. Field of the Invention
The present invention relates to an image forming device such as a facsimile machine, a copier and a printer (including a Multi Function Peripheral (MFP) having a facsimile function, a copy function and a printer function). More particularly, the present invention relates to an image forming device in which a paper feed cassette for feeding printing papers to a printing unit is removably inserted in a cassette accommodating portion of a device main body.
2. Description of the Related Art
A paper feed cassette includes a flapper (a pressing-up plate) which is elastically urged upward by an elastic urging member, such as a compression spring, provided on a bottom surface of the paper feed cassette. Accordingly, under a state in which the paper feed cassette is inserted in a cassette accommodating portion of device main body, a leading edge of an uppermost sheet of printing papers accommodated and stacked in the paper feed cassette elastically makes contact with a paper feed roller or a separating claw. In order to facilitate supplying of the printing papers in the paper feed cassette, the paper feed cassette also includes a locking member for maintaining the flapper at a prescribed pressed-down position against an urging force of the elastic urging member. The cassette accommodating portion of the image forming device includes a lock releasing member which unlocks the locking member when the paper feed cassette is inserted into the cassette accommodating portion.
In the image forming device including the paper feed cassette and the cassette accommodating portion as described above, when the printing paper runs out in the paper feed cassette or when a remaining amount of the printing papers in the paper feed cassette becomes small, the paper feed cassette is normally filled full with printing papers. Therefore, an elevating width of the flapper when being unlocked at an insertion of the paper feed cassette becomes small for a stacked thickness of the printing papers. As a result, an impulse when the leading edge of the uppermost sheet of the stacked printing papers elastically makes contact with the paper feed roller or the separating claw becomes small. However, for example, sometimes it is necessary to temporarily fill in B5-sized printing papers instead of generally used A4-sized printing papers. In such a case, only a necessary number of B5-sized printing papers are filled in. That is, only a few sheets of printing papers are filled in. Therefore, when the flapper is unlocked at the insertion of the paper feed cassette, the flapper receives an elastic restoration force of the elastic urging member and instantly jumps for a long elevating width from the prescribed pressed-down position to a position where the leading edge of the uppermost sheet of the stacked printing papers makes contact with the paper feed roller or the separating claw.
As a result, a large impulse and a large impulsive sound generate. Consequently, peripheral mechanisms may be damaged, or the printing papers may be displaced. Alternatively, an operator may feel uncomfortable or insecure. In particular, in case of a paper feed cassette capable of accommodating a large number of printing papers, the urging force of the elastic urging member is set great and the elevating width also becomes long. As a result, the impulse and the impulsive sound become even larger. A first conventional art and a second conventional art disclose a paper feed cassette including a buffer member for buffering the impulse when the flapper elevates by being unlocked.
The paper feed cassette disclosed in the first conventional art includes a locking member, a lock releasing member, and a damper mechanism for controlling an elevating speed of a flapper (a pressing-up plate). Since a new mechanism is required to be installed, a structure of the paper feed cassette becomes complex and the costs of the paper feed cassette increase. The paper feed cassette disclosed in the second conventional art includes a regulation member. When a flapper (a pressing-up plate) elevates rapidly, the regulation member catches the flapper before the flapper hits a separating claw. Accordingly, it is possible to prevent a deformation of the separating claw and a generation of the impulsive sound. However, the regulation member is required to be newly installed. In addition, the elevating width of the flapper leading to the regulation member is long. As a result, there still remains a problem of the impulse and the impulsive sound of the regulation member and the flapper.